# The molar mass of sodium chloride determined by osmotic pressure would be

$\begin{array}{1 1}58.5gmol^{-1}\\\text{more than }58.5gmol^{-1}\\\text{less than }58.5gmol^{-1}\\117.0gmol^{-1}\end{array}$

Answer : less than $58.5gmol^{-1}$
The molar mass obtained from a colligative property is the number average molar mass.This mass for NaCl will be $(23+35.5)gmol^{-1}/2=29.25gmol^{-1}$.